Formatting a number by a decimal

Question

I'm trying to transform an array of numbers such that each number has only one nonzero digit. so basically

"7970521.5544"

will give me

 ["7000000", "900000", "70000", "500", "20", "1", ".5", ".05", ".004", ".0004"]

I tried:

  var j = "7970521.5544"

  var k =j.replace('.','')

  var result = k.split('')

  for (var i = 0; i < result.length; i++) {
  console.log(parseFloat(Math.round(result[i] * 10000) /10).toFixed(10))
}

Any ideas, I'm not sure where to go from here?

Answer 1

Algorithm:

Split the number in two parts using the decimal notation.

Run a for loop to multiply each digit with the corresponding power of 10, like:

value = value * Math.pow(10, index); // for digits before decimal
value = value * Math.pow(10, -1 * index); // for digits after decimal

Then, filter the non-zero elements and concatenate both the arrays. (remember to re-reverse the left-side array)

var n = "7970521.5544"

var arr = n.split('.'); // '7970521' and '5544'
var left = arr[0].split('').reverse(); // '1250797'
var right = arr[1].split(''); // '5544'

for(let i = 0; i < left.length; i++)
  left[i] = (+left[i] * Math.pow(10, i) || '').toString();

for(let i = 0; i < right.length; i++) 
  right[i] = '.' + +right[i] * Math.pow(10, -i);

let res = left.reverse() // reverses the array
  .filter(n => !!n) 
// ^^^^^^ filters those value which are non zero
  .concat(right.filter(n => n !== '.0'));
// ^^^^^^ concatenation
  
console.log(res);

Answer 2

You can use padStart and padEnd combined with reduce() to build the array. The amount you want to pad will be the index of the decimal minus the index in the loop for items left of the decimal and the opposite on the right.

Using reduce() you can make a new array with the padded strings taking care to avoid the zeroes and the decimal itself.

let s = "7970521.5544"
let arr = s.split('')
let d_index = s.indexOf('.')
if (d_index == -1) d_index = s.length  // edge case for nums with no decimal

let nums = arr.reduce((arr, n, i) => {
  if (n == 0 || i == d_index) return arr
  arr.push((i < d_index) 
      ? n.padEnd(d_index - i, '0')
      : '.' + n.padStart(i - d_index, '0'))
  return arr
}, [])

console.log(nums)